This invention relates to a positioning control system which can be used for positioning control in various power units such as an electric motor and a hydraulic cylinder and, more particularly, to an improvement in lead compensation in the positioning control system and, more particularly, to employment of time data as a lead compensation parameter in such system and, further, to such system having a learning function.
In controlling a machine by detecting position of the machine by means of a cam switch, limit switch or the like mounted on the machine and performing necessary controls in response to position detection output, there arises time delay between a time point at which this position detection output is produced and a time point at which the control responsive to this position detection output is exercised upon the machine. Such time delay causes shifting of position in appearance at which the switch or the like device is actuated thereby giving rise to the inconvenience that an accurate control of the machine is hampered. For eliminating such inconvenience, it has been a general practice to perform compensation to shift the actuating position of the limit switch or the like or position detection data or positioning target value by an amount corresponding to the delay in time or operation. This compensation is generally called lead compensation.
The simplest example of lead compensation is mounting of a limit switch or the like detection device at a position shifted from a desired position by an amount of lead compensation. The amount of time delay however is not uniform but is varied depending upon the operation speed of the machine. The amount of lead compensation must therefore be varied in accordance with the speed of the machine so that the mounting position of the switch or the like must be changed each time the speed of the machine is changed.
For overcoming this inconvenience, there is a prior art system according to which a position detector capable of continuously detecting position of a machine is provided instead of using limit switch or the like and a target position detection output is obtained by comparing position detection data of the position detector with an established target position value. In this prior art system, lead compensation is achieved by detecting the speed of the machine, obtaining the amount of lead compensation in response to the detected speed and correcting position detection data or target position data in accordance with this amount of lead compensation. The principle of this system is shown in FIG. 7. In FIG. 7, a lead amount .theta.a is obtained by a lead amount operation circuit 1 in accordance with speed.nu. of the machine obtained by a speed detector 2 and lead compensation parameter a established depending upon operation conditions of the machine and lead compensation is achieved by adding the lead amount .theta.a and position data X detected by a position detector 3 together and thereby advancing, in appearance, data representing the present position of the machine by the lead amount .theta.a. In this case, the operation circuit 1 may be so constructed that the lead amount .theta.a is obtained by implementing operation of a predetermined function f (.nu.) in real time or that a memory prestoring lead amounts .theta.a corresponding to various speeds of the machine is provided and corresponding lead amount is read out in response to the speed .nu. of the machine.
The prior art system has the disadvantages that the provision of the speed detector results in high manufacturing cost, that in case the operation of the function f (.nu.) for obtaining the lead amount is performed in real time, operation tim required gives rise to time delay and that in case the speed is obtained by computing the position detection data, operation time required gives rise to time delay also.
It is, therefore, an object of the invention to provide a positioning control system having a lead compensation function which has eliminated these disadvantages of the prior art system.